The present invention relates to a coupling joint for an operative lever apparatus in which an angle of the inclination of a lever is detected by a rotary angle sensor for producing an electrical output representative of the angle.
A known operative lever apparatus of this sort is disclosed in Unexamined Japanese Utility Model Publication No. 62-140636.
That is, as shown in FIGS. 1 and 2, such an apparatus 1 has coupled thereto a lever 2 with a universal joint 3 so that the lever 2 may be freely inclined in a direction of X and in a direction of Y. In the apparatus 1, a pair of first rotary angle sensors 4 are provided in the X direction whereas a pair of second rotary angle sensors 5 are provided in the Y direction. A rotary shaft 4a for the pair of first rotary angle sensors 4 are jointed via a first gimbal 6 whereas a rotary shaft 5a for the second pair of rotary angle sensors 5 are jointed via second gimbal 7. The lever 2 is inserted through the respective elongate apertures 6a and 7a of the first and second gimbals 6 and 7 so that when the lever 2 is inclined in the X direction, the second gimbal 7 may be rocked to rotate the rotary shaft 5a of the pair of second rotary angle sensors 5 and that when the lever 2 is inclined in the Y direction, the first gimbal 6 may be rocked to rotate the rotary shaft 4a of the pair of first rotary angle sensors 4.
In such an operative lever apparatus, the respective rotary shafts 4a and 5a of the first rotary angle sensors 4 and the second rotary angle sensors 5 are coupled to the respective axial portions of the first and second gimbals 6 and 7 via coupling joints, respectively. These coupling joints may each be a modified Oldham joint which, as shown in FIG. 3, comprises a coupling member 8 in the form of a rectangular plate having a rectangular hole 8a to be fitted with a rectangular projection 4b, 5b of the respective rotary shaft 4a, 5a. A rectangular coupling member 8 is adapted to fit in a recess 9a formed at the end of each shaft 9 of the respective first and second gimbals 6 and 7.
With such a joint coupling, it is necessary that the rotary shaft 4a, 5a and the shaft 9 should be smoothly coupled together so that rotation of the shaft 9 can be transmitted to the first and second sensors 4, 5 with a high degree of precision.
For this reason, there is provided an interference at an engagement portion each between the coupling member 8 and the recess 9a and between the rectangular hole 8a and the projections 4b, 5b.
However, if the interference is made larger at the engagement portion between the rectangular hole 8a of the coupling member 8 and the projection 4b, 5b of the rotary shaft 4a , 5a , when the projection 4b, 5b is being engaged with the rectangular hole 8a , the coupling member 8 tends to deform. Since the opposing surface dimensions will be reduced, it follows that a spacing will be produced between the coupling member 8 and the recess 9a so as to develop a back-lash at an interface thereof.
More specifically, as shown in FIG. 4, the coupling member 8 is formed by a pair of first sides 8b and a pair of second sides 8c so as to be rectangular. Then, when the rectangular hole 8a is formed so that its width may be changed from L1 to L2, the amount of deformation S2 of the sides 8c will become larger and produce a spacing between each side 8c and the recess 9a so that a back-lash may be created at an interface between the coupling member 8 and the recess 9a. In order to prevent such a spacing from developing, it is necessary to increase the interference at the coupling portion between the coupling member 8 and the recess. By doing so, however, the ease with which they may be assembled will be reduced.
With the foregoing problems taken into account, it is an object of the present invention to provide a coupling joint for an operative lever apparatus, where if the interference at the engagement portion between the rectangular hole of the coupling member and the projecting portion of the rotary axis of the sensor is increased, the coupling member can be fitted in the engagement recess portion without materially producing a spacing between them, and thus the shaft of the gimbal and the rotary shaft of the rotary angle sensor can be coupled together without materially developing a back-lash at an interface between the coupling member and the projecting portion.